The present invention relates to a method of improving the control behavior of a brake system with anti-lock control, wherein the rotational behavior of the wheels is measured and evaluation and logical combining of the wheel rotational speed data permits producing a vehicle reference speed, wheel slip data and wheel acceleration data and other control parameters which are used to proportion and modulate the braking pressure.
Electronically controlled anti-lock brake systems (ABS) have gained in significance in the past years. Systems of this type are on the market in large numbers and various designs. In the majority of systems known in the art, the data required for anti-lock control are produced by measuring the rotational behavior of the vehicle wheels. A vehicle reference speed is determined by logically combining the signals originating from the individual wheels and can be taken into account as a reference quantity to calculate the wheel slip and other control parameters and, in addition, to set and modulate the braking pressure in the wheel brakes of the individual vehicle wheels.
Difficulties are involved in the identification of the actual control situation by way of the data furnished by the wheel sensors and the adjustment or modulation of the braking pressure in terms of an optimal braking behavior when the interpretation of the sensor signals is no absolute indicator of the instantaneous driving and control situation. Further, per se contradicting demands in terms of wheel stability (by pressure relief) and a short stopping distance (by a maximum possible braking pressure) must be satisfied in pressure modulation which is performed by the ABS controller on the basis of the so-called control philosophy, i.e., the predetermined algorithms, in response to the rotational behavior of the individual wheels.
There is a number of situations which are especially difficult to be identified by the ABS controller and which give rise to misinterpretations if no special measures are taken. For example, bumps and other disturbances in the road surface cause vehicle decelerations which are erroneously interpreted as locking tendency by the controller. Therefore, it is appropriate to analyze the rotational behavior of the wheels pursuant criteria of different types in order to discover contradictions and to protect individual control measures, especially those which are critical in terms of safety, according to different aspects and criteria.
An object of the present invention is to identify control situations where the braking pressure adjusted by the control is too low or is below the per se achievable optimum.